A conventional mobile communication system using CDMA (code division multiple access) method generally employs a plurality of methods to transmit data including moving picture data transmitted and received in application such as IP-TV phone or the like.
For example, the CDMA2000 standard defines three communication systems to transmit data: CDMA2000 1x that employs a circuit switching method; CDMA2000 1x EV-DO Rev.0 that employs a packet switching method and supports data rates (transmission speed) of uplink up to about 153.6 kbps and downlink up to about 2.4 Mbps; and CDMA2000 1x EV-DO Rev.A that is an accelerated Rev.0 system and supports data rates (transmission speed) of uplink up to about 1.8 Mbps and downlink up to about 3.0 Mbps (see “cdma2000 High Rate Packet Data Air Interface 3GPP2 C.S0024 Version 4.0”, 3GPP2, October 2002 (Section 8.5.6.1, Section 9.3.1.3.2.3.2) and “cdma2000 High Rate Packet Data Air Interface 3GPP2 C.S0024-A Version 1.0”, 3GPP2, March 2004 (Section 14.2.1.3.1.1, Section 14.3.1.3.1.1)). Moreover, CDMA2000 1x EV-DO Rev.A has a feature that a function for controlling QoS (Quality of Service) is added.
An initial connection in a mobile communication system will be described by referring to a sequence diagram shown in FIG. 5.
When a call connection request (ConnectionRequest) signal is transmitted from a wireless communication terminal to a base station, the base station which received the request signal transmits an AC Ack signal, a TrafficChannelAssignment signal and an RTC Ack signal back to the wireless communication terminal. The wireless communication terminal which received those signals transmits a TrafficChannelComplete signal to the base station. Thus, PPP (Point to Point Protocol) terminal authorization is performed between the wireless communication terminal and the base station. And then, PPP user authorization is performed between the wireless communication terminal and an IP packet terminating device (PDSN), and registration (Regist) is performed between the wireless communication terminal and SIP (Session Initiation Protocol). And then, QoS is established between the wireless communication terminal and the base station, and then RSVP negotiation (Resource reSerVation Protocol (RSVP) Negotiation) is performed. When transmission and reception of an Invite signal is performed between the wireless communication terminal and the communication protocol (SIP), the wireless communication terminal can start communication.
A connection (reconnection) of a wireless communication terminal from a standby state in the mobile communication system will be described by referring to a sequence diagram shown in FIG. 9. When a call ConnectionRequest signal is transmitted from the wireless communication terminal to a base station, the base station which received the signal transmits an AC Ack signal, a TrafficChannelAssignment signal and an RTC Ack signal back to the wireless communication terminal. When the wireless communication terminal which received those signals transmits a TrafficChannelComplete signal to the base station, the wireless communication terminal is connected to the base station, and therefore, the wireless communication terminal can start communication.
In a mobile communication system, when performing QoS, a wireless communication terminal basically requests a QoS rate of the maximum speed. However, there are cases that the QoS rate of the maximum speed cannot be acquired by reason that “resources are not sufficient since there is a large amount of connection to the base station” or the like.
In addition, in the mobile communication system, when performing QoS, a wireless communication terminal basically requests a QoS rate of the maximum speed. However, the QoS rate of the maximum speed cannot be acquired even when the wireless communication terminal which is not allocated to the QoS rate of the maximum speed and which connects to the base station transits to a standby state, and thereafter it connects again to the base station. In other words, the QoS rate is determined after the wireless communication terminal connects to a wireless channel, and the wireless communication terminal starts communication with the determined QoS rate. However, when a wireless channel (lower layer) is cut off due to effects of tunnel or the like, it becomes a dormant state, and in the dormant state, the lower layer is released and a high session maintains an active state. And then, when the wireless channel is recovered, the wireless communication terminal re-connects to the wireless channel. However, the QoS rate when reconnection is established is maintained at the same level with the QoS rate at the initial connection.